Piezo-electric crystal apparatus



June 24, 1930. A. CROSSLEY 1,766,036

PIEZO ELECTRIC CRYSTAL APPARATUS Filed April 14, 1927 a I l N V EN TOR.

2k A LZ/ a e d Cross Z? ATTORNEY Patented June 24, 1930 UNITED STATES PATENT OFFIQE ALFRED OROSSLEY, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR, BY MESNE ASSIGNMENTS, TO FEDERAL TELEGRAPH COMPANY, A CORPORATION OF CALI- FORNIA PIEZO-ELEOTRIG CRYSTAL APPARATUS Application filed April 14,

My invention relates broadly to piezo electric crystal apparatus and more particularly to a holder for piezo electric crystal elements.

One of the objects of my invention is to provide a construction of piezo electric crystal by which the condition of oscillation of a piezo electric crystal may be facilitated and oscillations of a relatively large amplitude sustained.

Another object of my inventlon is to provide a. construction of piezo electric crystal holder with means for centering the piezo electric crystal element therein for susta ning constant frequency oscillations with mmimumrestriction upon the crystal for securing maximum efliciency in the crystal operation.

Still another object of my invention is to provide a construction of mountingfor a piezo electric crystal element wherein the crystal is spaced from the inner walls of the mounting in such manner that absorption of space vibrations set up" about the piezo electric crystal element is substantially negligible.-

A further object of my invention is to provide a construction of mounting for piezo electric crystal elements in which the piezo electric crystal element is. spaced from the inside Walls of the container for a distance. substantially. equal to an odd multiple of a quarter wavelength of the air wave length coiyresponding to the resonant frequency of the or stal for reducing the absorption of energy li y reflection and reboundlng of space vibrations immediately adjacent the piezo electric crystal element.

My invention will be more clearly understood from the specification hereinafter following by reference to the accompanymg drawings wherein:

- Figure 1 is a plan view of one form of plezo electric crystal holder embodying the principles of my invention; Fig. 2 is a cross-sectional view through the crystal holder of Fig. 1 on line 2-2 thereof; Fig. 3 is a plan view of a modified form of piezo electric crystal holder construction in accordance with my invention; and Fig. 4 is a cross-sec- 1927. Serial No. 183,887.

tional view taken through the piezo electric crystal holder of Fig. 3.

I discovered that the space vibrations set up in the immediate vicinity of a piezo electric crystal element in its condition of oscillation may operate to absorb such a large percentage of energy from the piezo electric crystal element as to impair the oscillating condition of the element. Where the piezo electric crystal element is mounted within a container of the kind more fully described in my Letters Patent No. 1,572,773, dated February 10, 1926 and Letters Patent 1,619,854, dated March 8, 1927, the crystal during its condition of oscillation tends to establish space vibrations in the immediate vicinity of the piezo electric crystal element. Where the air space corresponds to one-half Wave length in air of the crystal frequency between the side walls of the crystal holder and the crystal surface, there is a tendency for the vibrations to produce a reenforcing effect on the crystal resulting in a change in the frequency of the output from the piezo electric crystal. By tapping the crystal holder and slightly changing the distance between the crystal and the side walls of the container it was found possible to avoid this shift in frequency. Aftera closer study of these phenomena it was found that a minimum effect on the frequency is produced when the crystal is separated from the side walls and top of the container by a'distance which is equal to one quarter the wave length of the space vibrations, such vibrations corresponding in frequency to the frequency of the piezo electric crystal element. I have found that equally satisfactory results are obtained by separating the piezo electric crystal element at distances of g, I

siderably reduced and the effect of the space vibrations upon the crystal with respect to L shift in frequency is substantially negligible.

' her 7 with the upper distance from to the drawings in more detail aracter 1 illustrates the bottom electrode for the iezo electric crystal holder on which electro e the piezo electric crystal element 2 is positioned with an upper electrode 3 touching the top surface thereof. The piezo electric crystal is mounted within a housing 4 having a top closure member 5 which carries contact member 6 to which connection is made through the flexible memelectrode 3. I provide a plurality ofinsulated members 8 in the form of small triangles having their apexes directed toward the center of the container and closely approaching the sides of the piezo electrical crystal elements 2 for centering the piezo electric crystal element within the holder while avoiding frictional contact with the iezo electric crystal element; The bases 0 the triangular members 8 abut against the side walls 4 of the container. The altitudes of each of these triangular members 8 is equal to an odd multiple of oneuarter the wave length of the piezo electric requency. That is to say, the altitudes of these triangular members 8 is such that the sides of the piezo electric crystal 2 may be spaced from the side walls of the container 4 through distances of or any other odd quarter wave length 4 4 the side of the crystal. Sim larly, the top surface of the piezo electric crystal element 2 is spaced at some odd quarter wave length multiple of the crystal frequency from the top of the piezo electric crystal holder.

In Fig. 2 I have shown a circular disc type piezo electric crystal element, and in this construction a circular housing 9 is provided surrounding the piezo electric cr stalelement 2. The piezo electric crystal e ement may be positioned for free vibration within the housing 9 by means of pegs 10 which extend from the lower electrode 1. The pegs 10 are located at a distance from the-inside walls of Referrin reference c h the housing 9 equal to an odd quarter wave length multiple of the crystal frequency which spacing I have determined will prevent the reflection of vibrations from impairing the oscillatory condition of the piezo electric crystal element. The top of the piezo electric cr stal element is spaced from the inside of tlie top of the container by selecting the depth of the chamber by regulating the length of the walls 4 in a manner similar to the spacing illustrated in Fig.2, that is by a distance which is equal to I or the odd quarter wave length of sound in air, where n is any whole number.

By virtue of the arrangement explained herein the formation of nodes at the inside walls of the piezo electric crystal holder is prevented and the vibrations from the piezo electric or stal element meet the inside walls or the inside of the top of the piezo electric crystalholder at an anti-node and the power in the reflected wave is so reduced that at the time that it is incident upon the piezo electric crystal element the element has in turn reached sucha position that a large potential force is available for opposing the feeble reflected energy, thereby eliminating the absorption of energy from the piezo electric crystal element.

The arrangement described herein has been found. to be extremely practical and piezo electric crystals arranged in accordance with the principles of my invention have been found to efficiently sustain high frequency oscillations.

What I claim as new and desire to secure by {setters Patent of the United States is as folows:

1. In a mounting for a piezo electric crystal element, a casing, comprising a base member constituting a conductive electrode and walls mounted upon said base member and supporting a top closure member and a piezo electric crystal element mounted upon said electrode and spaced from the walls of said casing for a distance substantially equal to an odd multiple of a quarter wave length of the air wave length corresponding to the frequency of said piezo electric or stal element for eliminating the absorption 0 energy from said piezo electric crystal element by space vibrations in the immediate vicinity of said piezo electric crystal element.

2. A piezo electric crystal ap aratus comprisin an electrode member, a housing supporte on a portion of said electrode member, a piezo electric crystal element having one surface thereof lyin in contact with said electrode member, said piezo electric cr stal element being s aced from the interior 0 said housin for a istance equal to an odd quarter of t e wave length of space vibrations immediatel surroundin said piezo electric crystal e ement for reducing the absor tion of energy from said piezo electric crysta element.

{3; A piezo electric c stal a paratus comprising a lower electro e member a housing supported on said lower electro e member, said housing being constituted by side walls and a top closure, a piezo electric crystal element centrally located on said lower electrode member, said top closure and side walls being spaced from said piezo electric crystal element for a distance equal to an odd quarter of the wavelength of space vibrations in the immediate vicinity of said piezo electric crystal elementfor reducing the absorption of energy from said piezo electric crystal element.

4. A piezo electric crystal apparatus comprising a housing including 'side walls and top and bottom closures, an electrode constituting said bottom closure, a piezo electric crystal element having one surface thereof lying in contact with said electrode, a second electrode arranged to establish connection with the opposite surface of the piezo electric crystal element, and means for spacing said piezo electric crystal element between said electrodes with respect to side walls and top closure constituting said housing with a distance between thelast mentioned surface of anti-node.

ALFRED CROSSLEY.

said'piezo electric crystal element and said top closure and between the sides of said piezo electric crystal element and said side walls equivalent to an odd quarter of the wave length of space vibrations set up within said housing in the vicinity of said piezo electric crystal element.

5. A piezo electric crystal apparatus comprising a housing including side walls and top and bottom closure members, a piezo electric crystal element disposed within said housing, and triangular shaped block members positioned between the sides of said piezo electric crystal element and the interior walls of said housing, said triangular shaped block members having altitudes equal to an odd quarter of the wave length of space vibrations established in said housing by said piezo electric crystal element. 4

6. A piezo electric crystal apparatus comprising a housing including side walls and top and bottom closure members, a piezo electric crystal element disposed within said housing, and triangular shaped block members having their apexes directed toward the sides of said piezo electric crystal element, with their bases in contact with the interior walls of said housing, the altitudes of said triangular shaped block members being equal to an odd quarter of the wave length of space vibrations established within said housing by said piezo electric crystal element.

-7. A piezo electric crystal apparatus comprising a housing, including top and bottom closure members and side walls located between said closure members, a piezo electric crystal element disposed within said housing, and block members, each having a width corresponding to an odd quarter of the wave length of vibrations established by said piezo electric crystal element in said housing, said block members being disposed between the sides of said piezo electric crystal element and the interior walls of said housing.

v 8. In a housing for a piezo electric crystal element, a conductive plate member, a wall structure supported upon and extending from said conductive plate member, a piezo electric crystal element and means for spacing said rystal element on said conductive plate 

